/* list 为双向循环链表 */
#include <list>
#include <iostream>

using namespace std;

int main(int argc, char **argv)
{
    list<int> l;

    l.push_back(10);
    l.push_back(20);
    l.push_back(30);

    list<int>::iterator it = l.begin();

    cout << *it << endl;
    it--;
    it--;
    cout << *it << endl;

    return 0;
}